VW Golf Oil Pressure light

I have a 1996 VW Golf that I bought in July of 2010. This car is an automatic. It needed a new engine shortly after I got it. After the engine was installed, I have a recurring problem where the oil pressure light comes on (first the light fades in and out, and then it is on consistently and there is an accompanying beeping). This usually happens when I have been driving it for over 45 minutes at a time and have been sitting in traffic. Last Friday it happened right near a VW specialized shop. They let it run, tested the oil pressure, and said that the car may have had too much oil and proceeded to drain about a quart out. They said the pressure was fine.

I got the car back today and drove it home. I had to run a few errands and was driving it for about an hour and a half (including stops). As I neared my house, the car was in the 2,000 rpm range. As I tried to accelerate into the 2,000 rpm range, the beeping started and the oil pressure light came on. After a bit of driving, the car would not go past 2,000 rpm unless I really tried to force it. When I went below 2,000 rpms that range the light went off. It still flickered a bit below the 2,000 rpm range, but the sound did not go on.

Any possibilities on what can be causing this? I really want to dump this car if it continues to be a problem like this.

Thanks,

Anthony

You say it got a new engine. Does this mean new as in brand new out of the crate or new as in a used engine that is new to that particular car?

Overfilling the oil by a quart will not affect the engine oil pressure and if they claimed this to be the case then maybe other things are not so fine.
Did they by chance tell you what the pressure was both at idle and at elevated RPMs with the engine warmed up?

Step One: Replace the oil pressure switch. If that fails,

Step Two: Switch to 20w-50 oil and sell the car…